Method for pumping a fluid

ABSTRACT

The invention concerns a method for pumping a fluid, for instance an oil effluent derived from a source adjacent to a well, towards an outlet, the well comprising a chamber extending substantially over the whole length of the well, and a pipe column passing through the chamber and communicating with it at one end, and, at an intermediate point on its length with the source. The invention comprises the following steps: filling, up to a predetermine height, the lower end of the chamber and of the pipe column with a first liquid with a density higher than that of the effluent; filling the chamber, between the predetermined height and the outlet, with a second liquid with a density lower than that of the first liquid, and injecting an additional amount of the second liquid in the chamber so as to displace the first liquid and the effluent, in order to bring the effluent up towards the outlet. The invention also concerns a pumping installation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for pumping a fluid and, morespecifically, to a method for pumping or raising hydrocarbons from anoil well.

The present invention also relates to an installation for pumping aliquid from an underground source.

2. Description of the Related Art

In some oil wells, the natural flow of hydrocarbons from the bottom tothe surface is not sufficient to allow or to sustain commercialproduction. This is due either to the viscosity or weight of theeffluents, or to a natural pressure at the bottom of the well which istoo low in comparison with the factors which oppose the raising of theseeffluents to the surface. In order to allow the well to be exploited ona commercial scale it is advisable to use a system for artificiallyraising the effluent, or a well-activation system. For example, a pumpmay be mounted at the lower end of a production tube located in thewell, or an installation for injecting gas into the bottom of the wellmay be provided. The latter type of installation, more commonly known asa gas lift, is used to lighten the column of hydrocarbons located in thewell in order to make it easier to raise to the surface.

However, the use of a pump at the bottom of a well, a place where thetemperatures and pressures are very high and where the surroundingenvironment may be very corrosive, may lead to breakdowns andmalfunctions of the activation equipment which, bearing in mind itslocation within the well, require lengthy and expensive interventions.Furthermore, the production of the well is halted during theseinterventions, and this leads to additional financial losses. Aninstallation for injecting gas into the bottom of a well is morereliable than the previous installation, but has the drawback ofrequiring a source of pressurized gas, for example a compressor with itsassociated pipework, on an isolated site.

Another assistance system consists in pumping hydrocarbons in from thesurface. Document EP-A-579497 describes a method for pumping liquid,from one end of a well to an outlet at the opposite end of the well, inwhich method the pressure of gas in one or more chambers is regulated insuch a way that these chambers fill with liquid. Next, a higher gaspressure is applied to each chamber so as to displace the liquid andconvey it towards the outlet. Each chamber is fitted with inlet andoutlet valves controlled from level detectors so as to control thedirection of flow of the liquid. According to this document, thechambers may either be superimposed on one another within the well, orplaced side by side at a point next to the well outlet.

Positioning the chambers so that they are superimposed in the well hasadvantages in that it makes it possible to have an installation which isless bulky and an optimized efficiency. By contrast, this type ofinstallation has drawbacks because superimposing the chambers, eachfitted with various valves and level detectors, requires one or morechambers to be withdrawn from the well when there is a breakdown orfailure in one of the lower chambers. Furthermore, the use of severalchambers, each fitted with valves and with level detectors, makesscheduling installation maintenance difficult.

Document U.S. Pat. No. 1,499,509 describes a method for pumping aneffluent from a not-very-eruptive oil well. According to this method,the effluent fills an annular space defined between the wall of the welland a production tubing which extends from the bottom of the well rightup to the surface. Once the annular space is filled with effluent,pressurized gas is conveyed from the surface into the top end of thisspace, and this displaces the effluent and causes it to rise up as faras the surface, inside the tubing.

This method has drawbacks in that it requires substantial installationsfor compressing, treating and transporting gas. Furthermore, the pumpingenergy is, for the most part, dissipated as heat, the result of thisbeing that it appreciably reduces the efficiency of the method.

SUMMARY OF THE INVENTION

The subject of the present invention is therefore a method for pumping afluid from a source at one end of a well to an outlet, which method issimple, reliable and allows use of an installation situated at thesurface and which is not very bulky.

To achieve this, the invention proposes a method for pumping a fluideffluent from a source (14) adjacent to a well (10) to an outlet (24),the well comprising a chamber (32) extending substantially along thelength of the well, and a tubing (18) passing through the chamber andcommunicating, at one end, with this chamber and, at an intermediatepoint along its length, with the source(14), characterized in that thismethod comprises the following stages:

filling the lower end of the chamber and of the tubing up to apredetermined height with a first liquid of higher density than theeffluent;

filling the chamber, between the predetermined height and the outlet,with a second liquid of lower density than the first liquid, and

injecting an additional quantity of the second liquid into the chamberso as to displace the first liquid and the effluent, in order to raisethe effluent up to the outlet.

The present invention therefore has the advantage of calling upon aninstallation in which the power unit is located at the surface, thusmaking its maintenance very easy and infrequent, and which is effectiveand reliable.

The subject of the present invention is also a pumping installation thatallows use of the pumping method.

To achieve this, the invention proposes an installation for pumping aliquid effluent from an underground source (14) comprising a well (10)extending from the surface (12) through the source and comprising achamber (32) extending along its entire length, a tubing (18) placed inthe chamber and communicating with this chamber at its lower end and, atan intermediate point along its length, with the source (14),characterized in that the chamber (32) and the tubing (18) are designedto be filled, to a predetermined height, with a first liquid of higherdensity than the effluent, the installation additionally comprising aseries of valves (38) intended to place the chamber (32) selectively incommunication with a pressurized source of a second liquid of lowerdensity than the first liquid, and in communication with a low-pressurereservoir for this first liquid.

Other features and advantages of the present invention will become clearfrom reading the following description given by way of non-limitingexplanation, with reference to the appended drawings.

BRIEF DESCRIPTION OF THE FIGURES OF DRAWINGS

FIG. 1 is a diagrammatic sectional view of a well according to a firstembodiment of the invention; and

FIG. 2 is a diagrammatic sectional view of a second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, a well depicted overall as 10 which, in the exampleillustrated, is an oil well, extends from the surface 12 of the groundthrough a layer of oil-bearing rock 14. The lower end 15 of the well issituated approximately XX m below the layer of rock 14. The well 10 hasa casing 16 extending along the well, and a production tubing 18extending from the surface 12 as far as the lower end 15 of the well.The tubing 18 comprises, at a point approximately 100 m from the surface12, a safety valve 20. At its upper end, the tubing 18 has a series ofproduction valves 22, or "Christmas tree" intended to control theproduction rate of the well. This series of valves communicates with aproduction pipe 24 forming the well outlet.

The well 10 and the tubing 18 extend beyond the layer of oil-bearingrock 14, the tubing 18 opening into this rock via a pipe 26 fitted witha non-return valve 28. The upper end of the well 10 is closed by a seal30 for suspending the tubing or "tubing hanger". The annular space 32defined between the casing 16 and the tubing 18 may be selectivelyplaced in communication with a high-pressure liquid source 34 and alow-pressure liquid reservoir 36 by a series of control valves 38,safety valves 40 and a pipe 42 which passes through the seal 30. Asafety valve 44 may advantageously be mounted at the end of the pipe 42.A non-return valve 46, placed in the tubing 18 at a point immediatelyabove the pipe 26, allows fluid to flow through the tubing only from thebottom towards the surface.

The pool in the layer 14 is not very eruptive, that is to say that thepressure exerted by the pool allows the effluent to be raised to anintermediate level N in the well. In order to raise the effluent to thelevel N as far as the surface, the pumping method according to theinvention is used.

This method consists in placing a first liquid, of high density, at thelower end of the well so that it fills the annular space and the lowerend of the tubing 18 up to a level A. Then, the empty volume of theannular space 32 is entirely filled with a second liquid from thehigh-pressure source 34 and of lower density than the first liquid. Thepressure exerted by the second liquid causes the level of the firstliquid to drop, in the annular space 32, from the level A to a lowerlevel B, the result of this being that the level of the first liquid inthe tubing 18 rises from the level A to a higher level C. The interiorof the tubing 18 between the level C and the level N contains effluentfrom the layer of rock 14.

Next, in order to displace the effluent in the tubing 18 towards thesurface, an additional volume of the second liquid is conveyed into theannular space, the result of this being to drop the level of the firstliquid by a distance d from the level B down to a lower level E. Thislower level is slightly above the open end of the tubing 18. The levelof the first liquid rises, by a distance h, as far as a maximum level G,just below the pipe 26. Then, in order to complete a pumping cycle, thecontrol valve 38 is operated to place the annular space 32 incommunication with the low-pressure reservoir 36. The static pressureexerted by the column of the first liquid in the tubing 18 on the secondliquid delivers this latter liquid into the low-pressure reservoir 36,the liquids tending to return to their starting levels B and C. Theeffluent which has been raised in the tubing towards the surface has noopportunity of dropping back down because of the action of thenon-return valve 46. When the first liquid in the tubing drops back fromits maximum level G to its level C, it creates a depression in thetubing 18, below the non-return valve 46, and this tends to increase thespeed at which the effluent flows from the rock 14 into the tubing 18.

Once the liquids have reverted to their starting levels B and C, and thetubing below the non-return valve 46 is filled with effluent, thepumping cycle can recommence, simply by reversing the position of thecontrol valve 38 in order to place the annular space 32 back incommunication with the high-pressure source 34. On each pumping cycle,the effluent is raised up the tubing 18 by a height h.

The use of the first liquid of high density allows it to act as a returnspring for the second liquid of lower density. By reverting to itsstarting level at the end of a cycle, the first liquid delivers thesecond liquid to the low-pressure reservoir and allows a furtherquantity of effluent to enter the tubing. The increase in size of thecompressor used to feed the high-pressure source with the second liquid,which is needed by the additional charge of the first liquid is small,the size of this compressor being nonetheless smaller than the oneneeded for a pumping method using a gas, as described in document U.S.Pat. No. 1,499,509.

FIG. 2 depicts a second embodiment which differs from that of FIG. 1 inthat it comprises a first casing 16 and a second casing 50 which definebetween them an annular chamber 52 delimited by two annular seals 55 and56. The annular chamber is open towards the layer of oil-bearing rock 14and communicates via a pipe 58 fitted with a non-return valve 60, with achamber 62 placed outside the tubing 18. The tubing 18 has two openings64 towards the chamber 62 and, in addition, is fitted with a non-returnvalve 66 at a point immediately above the chamber 62. The pumping methodusing this embodiment is approximately the same as the one employed inthe installation of FIG. 1.

The installation for pumping a liquid effluent shown in FIGS. 2A to 2Dis intended to be used on existing wells, that is on wells alreadyfitted with a production tubing. FIGS. 3A to 3D show an installation forpumping liquid effluent which is adapted to be installed on a well whichhas not yet been completed or on one on which the production tubing isintended to be changed.

At a point in the well 10, the tubing separates into two parallel tubes82, 84, of which one 82, extends through a packer 54 and communicateswith chamber 50, and the other, 84, communicates with the annular space32 at a point preferably immediately above packer 54. Tube 82 is fittedwith a non-return valve 60 which causes the effluent to flow only in thedirection of arrow 62.

The method of pumping the effluent used in the installation of FIG. 3 issimilar to that used with the installation of FIG. 2.

NUMERICAL EXAMPLE

As the method for pumping according to the invention uses liquid as apumping means, the loss of pumping energy in thermodynamic phenomena isconsiderably reduced. Furthermore the use of the first liquid of highdensity, which tends to revert to its starting level by delivering thesecond pumping liquid to its reservoir, further reduces the energyconsumption of the method.

What is claimed is:
 1. Method for pumping a fluid effluent from a sourceadjacent to a well to an outlet, the well comprising a chamber extendingsubstantially along the length of the well, and a tubing passing throughthe chamber and communicating, at one end, with this chamber and, at anintermediate point along its length, with the source, this methodcomprising the following stages:filling the lower end of the chamber andof the tubing up to a predetermined height with a first liquid of higherdensity than the effluent; filling the chamber, between thepredetermined height and the outlet, with a second liquid of lowerdensity than the first liquid; and injecting an additional quantity ofthe second liquid into the chamber so as to displace the first liquidand the effluent, in order to raise the effluent up to the outlet. 2.Method according to claim 1, comprising the additional stage of placingthe chamber in communication with a low-pressure reservoir of secondliquid so as to allow the second liquid to flow out of the chamber, thefirst liquid running down inside the tubing towards its predeterminedheight.
 3. Installation for pumping a liquid effluent from anunderground source comprising a well extending from the surface throughthe source and comprising a chamber extending along its entire length, atubing placed in the chamber and communicating with this chamber at itslower end and, at an intermediate point along its length, with thesource, wherein the chamber and the tubing are designed to be filled, toa predetermined height, with a first liquid of higher density than theeffluent, the installation additionally comprising a series of valvesintended to place the chamber selectively in communication with apressurized source of a second liquid of lower density than the firstliquid, and in communication with a low-pressure reservoir for thisfirst liquid.